Estimation method of earthwork excavation using shield tunneling data -- a case study of Chengdu Metro

The occurrence of over-excavation or under-excavation in tunnel construction poses significant safety risks. Moreover, there is currently no automatic estimation method available for real-time estimation of earthwork excavation, particularly in the case of shield tunnels. In this study, we tracked the excavation process of Chengdu Metro Line 19, acquired tunneling parameters and earthwork excavation data using various sensors, and subsequently proposed an automatic estimation method that combines Bayesian optimization (BO) and gradient boosting regression tree (GBRT) algorithm. The results of our case study indicate that the BO-GBRT model improves the performance of earthwork excavation estimation, reducing the residual after each calculation with a root mean square error (RMSE) of 1.712 and mean absolute error (MAE) of 1.331. Furthermore, compared to other machine learning methods, the proposed BO-GBRT model demonstrates superior estimation performance. Additionally, the importance distribution of input parameters reveals that propulsion pressure, foam pressure, and rotation speed are the most critical factors affecting earthwork excavation. Overall, the proposed automatic estimation method shows great promise as a tool for efficiently estimating earthwork excavation in shield tunnel construction

Advanced Underground Space Technology

The recent development of underground space technology makes underground space a potential and feasible solution to climate change, energy shortages, the growing population, and the demands on urban space. Advances in material science, information technology, and computer science incorporating traditional geotechnical engineering have been extensively applied to sustainable and resilient underground space applications. The aim of this Special Issue, entitled “Advanced Underground Space Technology”, is to gather original fundamental and applied research related to the design, construction, and maintenance of underground space

Risk analysis for tunneling projects

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 574-589).Tunnel construction is increasing world wide. Although the majority of tunnel construction projects have been completed safely, there have been several incidents that have resulted in delays, cost overruns, and sometimes more significant consequences such as injury and loss of life. To help eliminate these accidents, it is necessary to systematically assess and manage the risks associated with tunnel construction. In order to better understand the conditions under which accidents occur, a database of 204 tunnel construction accidents was assembled. This is the most comprehensive database known to date. The database was analyzed to better understand the causes of accidents. Influence diagrams were constructed containing the main factors, and the interactions between them. These served as the basis of the risk assessment methodology presented in this work. The risk assessment methodology consists of combining a geologic prediction model that allows one to predict geology ahead of the tunnel construction, with a decision support model that allows one to choose amongst different construction strategies the one that leads to minimum risk. The geologic prediction model is based on Bayesian networks because of their ability to combine domain knowledge with data, encode dependencies among variables, and their ability to learn causal relationships.(cont.) The combined geologic prediction - decision support model was then applied to the Porto Metro, in Portugal. The results of the geologic prediction model were in good agreement with the observed geology, and the results of the decision support model were in good agreement with the construction methods used. More significant, however, is the ability of the model to predict changes in geology and consequently changes in construction strategy. This was shown in two zones of the tunnel were accidents occurred, where the model predicted an abrupt change in geology, and the construction method should have been changed but was not. Using the model could have possibly avoiding the accidents. This risk assessment methodology provides a powerful tool with which planners and engineers can systematically assess and mitigate the inherent risks associated with tunnel construction.by Rita L. Sousa.Ph.D

Report of the Asilomar 3 LDR Workshop

The conclusions and recommendations of the workshop held to study technology development issues critical to the Large Deployable Reflector (LDR) are summarized. LDR is to be a dedicated, orbiting, astronomical observatory, operating at wavelengths from 30 to 1000 microns, a spectral region where the Earth's atmosphere is almost completely opaque. Because it will have a large, segmented, passively cooled aperture, LDR addresses a wide range of technology areas. These include lightweight, low cost, structural composite reflector panels, primary support structures, wavefront sensing and adaptive optics, thermal background management, and integrated vibration and pointing control systems. The science objectives for LDR present instrument development challenges for coherent and direct arrayed detectors which can operate effectively at far infrared and submillimeter wavelengths, and for sub-Kelvin cryogenic systems

Computational and Numerical Simulations

Computational and Numerical Simulations is an edited book including 20 chapters. Book handles the recent research devoted to numerical simulations of physical and engineering systems. It presents both new theories and their applications, showing bridge between theoretical investigations and possibility to apply them by engineers of different branches of science. Numerical simulations play a key role in both theoretical and application oriented research

Low-frequency elastic properties of glasses at low temperatures : investigations with double-paddle oscillators based on a dc-SQUID readout

Im Rahmen dieser Arbeit wurden niederfrequente Messungen der elastischen Eigenschaften von Gläsern (Quarzglas und BK7) bei tiefen Temperaturen mittels mechanischer Oszillatoren durchgeführt. Hauptschwerpunkt lag hierbei auf der experimentellen Entwicklung einer neuartigen Auslesetechnik für sogenannte Double Paddle Oszillatoren innerhalb eines Verdünnungskryostaten. Der induktive Detektionsmechanismus basiert hierbei auf der hohen Sensitivität von kommerziell erhältlichen dc-SQUIDs. Die Überlegenheit dieser Technik gegenüber der konventionellen kapazitiven Methode wurde durch Messungen an verschiedenen Gläsern demonstriert. Bereits in diesen ersten Messungen konnte die Sensitivität um mehr als eine Größenordnung gegenüber der kapazitiven Technik verbessert werden. Mit Hilfe des neuen Detektionsmechanismus wurden die relative Schallgeschwindigkeitsänderung und die innere Reibung von amorphem SiO2 und BK7 im Temperaturbereich zwischen 5mK und 1K für mehrere Frequenzen untersucht. Die Ergebnisse an Quarzglas stehen in guter Übereinstimmung mit konventionell durchgeführten Messungen, während für BK7 leichte Abweichungen zu früheren Messungen bei tiefsten Temperaturen beobachtet wurden

Investigation of Magnetic Adatoms with Scanning Tunneling Techniques

In this work, magnetic atoms on surfaces are studied with low-temperature scanning tunneling microscopy. Motivated by the idea to use single atoms as magnetic bits, the factors that allow or prevent long-term stability of their magnetic moments are investigated. Lifetimes of up to several minutes can be achieved for the magnetic moments of holmium atoms on a Pt(111) surface, resulting from the combined symmetries of the system. Corresponding theoretical calculations are presented and evaluated

Behaviour of segmental tunnel lining under static and dynamic loads

The aim of the research thesis is to provide a three-dimensional numerical model suitable to interpret the static and dynamic behaviour of a kind of segmental tunnel lining in soft soil. The static performance of the structure is investigated during the tunnel construction, involving the main tunnelling loads, obtaining the evolution of the state of stress and strain in the lining. The dynamic performance of segmental lining has been investigated both under uniform and not uniform seismic loads. In the case of uniform seismic load, pseudo static and full dynamic approaches have been compared, while non-linear coupled analysis have been used to investigate the post-earthquake lining condition. A study of the seismic vulnerability of such structures has been conducted based on fragility curves for different levels of damage. A procedure for the forecast method of risk assessment has been proposed for the case of segmental tunnel lining assuming as critical damage parameter the longitudinal joints rotation. Furthermore, a study of feasibility of Earthquake Early Warning System, EEWS, based on thresholds has been conducted through a probabilistic and a real-time approach for such tunnel structure. The coupling effect of multi-directional seismic motion both in transversal and longitudinal direction of the tunnel has also taken into account in the evaluation of dynamic tunnel behaviour. A comparison between the effect of synchronous and not synchronous seismic motion along the tunnel axis has been done in terms of dynamic increment of the components of forces in the lining

Experiments in tunnel-soil-structure interaction

Urbanisation will require significant expansion of underground infrastructure, which results in unavoidable ground displacements that affect the built environment. Predicting the interaction between a tunnel, the soil and existing structures remains an engineering challenge due to the highly non-linear behaviour of both the soil and the building. This thesis investigates the interaction between a surface structure and tunnelling-induced ground displacements. Specifically, novel three-dimensionally printed building models with brittle material behaviour, similar to masonry, were developed and tested in a geotechnical centrifuge. This enabled replication of building models with representative global stiffness values and realistic building features including strip footings, intermediate walls, a rough soil-structure interface, building layouts and façade openings. By varying building characteristics, the impact of structural features on both the soil and building response to tunnelling in dense sand was investigated. Results illustrate that the presence of surface structures considerably altered the tunnelling-induced soil response. The building-to-tunnel position notably influences the magnitude of soil displacements and causes localised phenomena such as embedment of building corners. An increase of the façade opening area and building length reduces the alteration of the theoretical greenfield settlements, in particular the trough width. Moreover, the impact of varying the building layout is discussed in detail. For several building-tunnel scenarios, building distortions are quantified and the crucial role of building features is demonstrated. Structures spanning the greenfield inflection point experienced more deformation than identical structures positioned in either sagging or hogging, and partitioning a structure either side of the greenfield inflection point is shown to lead to unconservative damage assessments. Results also quantify the significant extent to which structural distortions increase as façade openings and building length increases. Observed building damage and cracking patterns confirm the reported trends. The experimental results are used to evaluate the performance of available methods to assess the behaviour of buildings to tunnelling. Predictions ignoring soil-structure interaction are usually overly conservative, while approaches based on the relative stiffness of a structure and the soil result in inconsistent predictions, though some methods performed better than others. Practical improvements to consider structural details when assessing this tunnel-soil-structure system are finally proposed.Engineering and Physical Sciences Research Council (grant EP/KP018221/1), Crossrai

Lichtemission aus Mehrelektronenprozessen im Rastertunnelmikroskop

Light emission from noble metal junctions in a scanning tunneling microscope (STM) was investigated. The main subtopics are the determination of the local electronic temperature at the STM junction and light emission from multi-electron processes. A normalization scheme was derived in this thesis, based on the established model of single-electron STM light emission and experimental observations. The normalization was then applied to extract temperature information from STM light spectra. Temperatures in the order of 10s of Kelvins, depending on the applied bias and current, were found, in contrast to the results of many 1000s of Kelvins found in other publications. Using the normalization scheme, it was shown that the light intensity at these photon energies cannot be attributed to the thermal emission of an electron gas at elevated temperature and is instead to be interpreted as the result of electron-electron interaction. Measurements of light emission from a STM junction at photon energies more than two times the cutoff-energy of single-electron processes are shown for the first time. Distance dependent measurements prove a qualitatively different behavior of light emission at different photon energies ranges. Bias dependent measurements reveal a change of the slope of the spectra at distinct bias dependent thresholds. A quantitative model for light emission from multi-electron processes is developed. This semi-empirical extension of the one-electron case is in excellent agreement with spectra in most of the measured photon energy range. Deviations can be attributed to detection artifacts due to the low intensity of the light emission at high photon energy. The conductance dependence of the light intensity in each photon energy range is explained by the model in terms of Landauer-Büttiker conduction channels, in agreement with shot-noise measurements. Compatibility of the model with two alternative approaches found in the literature is shown.Diese Arbeit behandelt Lichtemission von Edelmetallkontakten im Rastertunnelmikroskop (STM). Wesentliche Unterthemen sind die lokale Elektronentemperatur und Lichtemission aufgrund von Mehrelektronenprozessen. Es wurde ein Normierungsverfahren entwickelt, ausgehend vom bereits bekannten theoretischen Modell der Einzelelektronen-Lichtemission im STM, sowie von experimentellen Beobachtungen. Die Normierung wurde dann angewendet um Temperaturinformationen aus STM-Lichtspektren zu gewinnen. In Abhängigkeit von Spannung und Strom wurden Temperaturen in der Größenordnung von einigen 10 Kelvin gefunden. Dies steht im Kontrast zu Temperaturen von vielen 1000 Kelvin, welche in anderen Veröffentlichungen gefunden wurden. Mit dem Normierungsverfahrens wurde gezeigt, dass STM-Lichtspektren bei hohen Photonenenergien nicht einfach durch thermische Emission eines heißen Elektronengases erklärt werden können. Zum ersten Mal werden Lichtspektren aus dem Rastertunnelmikroskop bei Photonenenergien von mehr als dem doppelten der höchsten Energie von Einzelelektronenprozessen gezeigt. Abstandsabhängige Messungen zeigen ein qualitativ unterschiedliches Verhalten bei verschiedenen Photonenenergien auf. Normierte Lichtspektren bei verschiedenen Spannungen zeigen eine Änderung der Steigung bei bestimmten spannungsabhängigen Energien. Es wurde dann ein quantitatives Modell entwickelt, welches die Lichtemission aufgrund von Mehrelektronenprozessen beschreibt. Diese halbempirische Verallgemeinerung des Einzelelektronenmodells ist über einen weiten Photonenenergiebereich in hervorragende Übereinstimmung mit gemessenen Spektren. Abweichungen können als Messartefakte aufgrund der niedrigen Lichtintensitäten erklärt werden. Die Abhängigkeit der Lichtintensität vom Leitwert des Kontaktes wird im Rahmen von Landauer Büttiker-Leitungskanälen erklärt. Die Vereinbarkeit des hier entworfenen Modells mit zwei alternativen theoretischen Ansätzen wird gezeigt